Hard coating preparation having hard coating layer made from sugar/sugar alcohol is defective not only in poor shock resistance such as shown by cracks on the surface of easily broken coating layer due to poor adhesion of sugar/sugar alcohol crystals respectively forming a coating layer, lack of flexibility in obtained coating layer, softness of the coating layer, etc. but also in high percentage of wasted coating liquid due to poorly adhering to the coating center while adhering more to the coating pan during production.
Such problems are marked in accordance with the increase of sugar/sugar alcohol content in coating layer.
Various additives are proposed to be used in the art to cover such defects of a coating layer made from sugar/sugar alcohols.
For example, water soluble macromolecular substances such as pullulan, gelatin, gum arabic are used as coating reinforcing agents in producing hard coating preparations having a coating layer with maltitol (see Japanese Patent Publication No. 7-55898).
However, the above substances used as coating reinforcing agents are newly defective, as they are difficult to handle due to high increase in viscosity when put in water solution, coating layer is browned with lapse of time, it takes long time for formation of coating layer, etc.
Moreover, those coating reinforcing agents are very expensive, as another disadvantage.
Then, use of xylitol for coating has been disclosed (see Japanese Patent Publication No. 5-14535).
However, it requires a plurality of additives such as film forming agent, binder, and filler as ingredients other than xylitol. In addition, coating liquid does not spread well when sprayed on the surface of coating center due to high viscosity of coating liquid, cracking the surface of the coating layer and failing to finish a pretty appearance of the product.
In other words, the object of the present invention is to provide a hard coating preparation having a hard coating layer, unbreakable, made from specific sugar/sugar alcohols, with low waste of coating liquid when forming the coating layer.